FIG. 39 illustrates a known smart system technology of the related art. According to the technology, a user 91 of a vehicle 90 carries a portable device 92 and approaches the vehicle 90. The portable device 92 receives request signal Req transmitted from the vehicle 90. Based on reception of this request signal Req, the portable device 92 transmits answer signal Ans to the vehicle 90. Based on reception of this request signal Req, the vehicle performs smart drive (either or both unlocking a door of the vehicle 90 and starting a vehicle drive apparatus). A receivable range of request signal Req transmitted from the vehicle 90 is limited to vicinity 93 of the vehicle. The purpose is to prevent the smart drive from being activated when the portable device 92 is distant from the vehicle 90.
Such a smart system technology may be subject to relay station attack (hereinafter referred to as RA) that enables communication between the portable device 92 and the vehicle 90 using a relay station and allows the vehicle 90 to perform smart drive even if the portable device 92 is distant from the vehicle 90.
FIGS. 40 and 41 illustrate the relay station attack. An RA relay station 94 is placed in a communicable range 93 of request signal Req. An RA relay station 95 is placed near a portable device 95. The RA relay station 94 receives request signal Req transmitted from the vehicle 90 and transfers request signal Req to the RA relay station 95. The RA relay station 95 receives the transferred signal and transfers it to the portable device 92. The vehicle 90 directly receives answer signal Ans transmitted from the portable device 92 by way of no relay station as illustrated in FIG. 40 or receives answer signal Ans by way of relay stations 96 and 97 as illustrated in FIG. 41.
Patent document 1 describes the technology that counteracts the relay attack including the RA relay station. The technology uses the fact that the RA relay station performs modulation and demodulation during the transfer to increase the communication relay time. The technology determines intervention of an RA relay station if an increase in the communication relay time differs from an allowable time range of the delay time estimated in the normal smart system operation. The technology thereby inhibits the smart drive.